Variable voltage generator



April 1949- F.. D. SNYDER I 2,467,784

VARIABLE VOLTAGE GENERATOR Filed March 20, 1947 VG MF LM IHVHI K HITNESSES- I INVENTOR figzfif d fieaer/ck D. Snyder.

- fut/5 ATTORNEY Patentecl Apr. 19, 1949 VARIABLE VOLTAGE GENERATORFrederick D. Snyder, Milton, Mass, assignor to Westinghouse ElectricCorporation, East Pittsburgh, Pa., a corporation of PennsylvaniaApplication March 20, 1947, Serial N0. 735,860

9 Claims.

My invention relates to a Ward-Leonard type of speed control for adirect-current motor.

In certain applications utilizing a variable voltage source of directcurrent for a motor, it is often highly desirable to obtain slow andsmooth successive motor accelerations from the same slowest speed to anypreselected higher speeds.

One broad object of my invention is the provision of automaticallyslowly and smoothly accelerating a direct-current motor from standstill,or a given slow inching speed to a selected high speed.

Another object of my invention is the provision of substantiallyautomatically successively accelerating a direct-currentmotor from aselected slow speed to any higher speed, within the range of the controlapparatus, selected between successive accelerations.

It is also an object of my invention to smoothly accelerate a motor bymeans of a Ward-Leonard control from a given low speed to anypreselected higher speed.

A further object of my invention is the provision of substantiallyautomatically altering the speed of a direct-current motor back andforth from one fixed low speed and a selected higher speed.

Other objects of my invention will become more apparent from a study ofthe following specification and the accompanying drawing, in which thesingle figure constitutes a diagrammatic showing of my invention.

In my system of control, I provide a manually operable rheostat 42having an adjustable control, or lead 43, for preselecting any one of aplurality of given speeds for motor LM, the load driving motor, and Iprovide a motor-operated rheostat 19 of the same design characteristicsas rheostat 42.

During acceleration of motor LM, the arm 23 is slowly movedcounterclockwise to increase the voltage of generator VG. Thearrangement is such that when arm 23 holds a position on rheostat [9corresponding to the speed setting of lead 43, the movement of thecontact 2] on rheostat l9 ceases. The motor LM thus continues to operatebut at a fixed speed determined by the setting of lead 43.

A still better understanding of my contribution to the art may be hadfrom a study of typical operating cycles. If the circuits shown in thefigur are considered as deenergized, except for buses l, 9 and I6, andthe attendant wishes to use the apparatus he actuates the Slow pushbutton, or switch, 6. This operation establishes a circuit from bus Ithrough conductor 2, actuating coil 3 of relay 4, contacts 5, closed bythe Slow push button, or switch, 6, stop push button I, conductor 8 tobus 9. The starting always is to proceed through a preliminary slowspeed so that the Slow push button 6 is the manually operable startingswitch as well.

Operation of relay 4 causes the closing of contacts I0. The relay 4 thusremains actuated independent of the position of switch 6, which may thusbe released as soon as relay 4 has operated. The relay 4 also closescontacts l2. This operation establishes a circuit from energizedconductor 2 through actuating coil ll of the main starting contaotor C,through contacts 12 to energized conductor 8. The operation of contactorC causes the closing of contacts l3, l4, and I5 to thus connect themotor M of the motor generator set MG to the buses I, 9 and I6.

The motor M thus presently brings the variable Voltage generator VG andthe exciter generator EG to full speed. To obtain the requisite slowspeed for the load driving motor, it is, of course, important that theexcitation of the variable voltage generator at this stage of operationbe a minimum. How this is accomplished will become apparent presently.

From an inspection of the figure, it will be apparent that the negativeterminals of the generators VG and EG are connected together. Conductor20 will thus be at the same negative potential, and the respectivepotentials of conductors l8 and 24 will thus be dependent of the voltageof the exciter generator EG and the voltage of the variable voltagegenerator VG. Since the exciter field EF and its series-connectedrheostat I1 and the motor field MF are directly across the exciterarmature terminals, namely conductors l8 and 20, the voltage ofgenerator EG will be at full value and the motor LM will be fullyexcited. The generator field GF will however be energized at a minimumvalue by a circuit which may be traced from conductor I8 through all ofthe sections of the generator field control rheostat I9, the generatorfield GF to conductor 20.

The resistance value of rheostat I9 is controlled by the position of thecontact 2|, connected to lead 22, and mounted on the arm 23 actuated bythe rheostat motor RM. The arm 23 during this stage of operation is inthe position shown. This is the all-resistance-in position. Why the arm23 must necessarily be in the position shown for this stage of operationwill become apparent hereinafter.

Since the excitation of the field GE is a minimum, the voltage acrossconductors 24 and is a minimum. The motor LM thus operates at its slow,or inching, speed.

The manually operable speed selecting rheostat 42, and the resistor 44connected in series with the rheostat, are connected directly acrossconductors l8 and 20. The rheostat 42 is similar in electrical and somemechanical characteristics to the motor-operated rheostat l9 and theparticular position of the connecting arm 43 on the resistor sections ofrheostat 42 normally determines the high-speed setting for the motor LM,but since contacts 41 are, at this stage of operation, open, theposition of the arm 23 has no ef feet in selecting a high-speed setting.

The resistor 44 has a resistance value so selected with reference to theresistance value of the resistor 45 that when the voltage drop fromjunction 30 through the actuatin coil 3| of the contact making voltmeterV to the junction 32 is zero for the particular high-speed selectionmade by the arm, the movable contact 25 of the voltmeter V holds theposition shown with reference to contacts 2%. However, since contacts Mare open, junction 3i? will be sufliciently positive with respect tojunction to effect the operation of the contact making voltmeter V.Contact 25 will thus remain in the position shown.

The contact making voltmeter, which may be of any standard design, will,since the potential drop is from junction 32 to junction 30., actuateits movable contact 25 clockwise to engage contact 50. This will,however, be of no effect since the contacts 48 of the limit switch 49,are open. The motor LM is thus, by reason of the low voltage ofgenerator VG slowly and smoothly accelerated from zero speed to theinching speed.

Voltage relay 33 has its actuatin coil connected directly across theconductors 24 and 20. Its characteristics are 50 selected that it is notactuated as long as the voltage of generator VG is such as to provideonly an inching speed for motor LM.

To effect the fast or selected speed of operation of motor LM, the Fastpush button, or switch, 35 is actuated. This operation closes a circuitfrom conductor 2, through coil 33 of relay 34, switch 35, conductor36,.contacts 3'! of voltage relay 33, conductor 39, switch 5, contacts Iof relay 4, and the Stop switch 'I to conduGEQr 8.

Operation of relay 34 closes contacts 40. This operation makes theenergization of coil 33 independent of the position of contacts3'i.Relay 34 also closes contacts 4|. This operation shunts a portion ofrheostat 42 to thusmake the speed setting of the arm 43 efiective.Junction 30 thus becomes more positive since the resistance drop acrossresistor 44 in relation to the drop across resistor 45 is increased. Acurrent thus flows from junction 36 through coil 3| to junction 32.

This current flow through the actuating coil 3| of the contact makingvoltmeter causes the contact 25 to engage contact 26. A circuit isfthusestablished from conductor 18 through contacts 25 and 26, the contacts21 of the high voltage limit switch 28, field 29, and the rheostat motorRM to conductor 20. The rheostat motor RM thus operates the arm 23counterclockwise shifting the contact 2! connected to lead 22 to shuntmore and more resistor sections of the rheostat l9.

The voltage of generator VG thus slowly and gradually increases, thusincreasin the speed of motor LM. As soon as the arm 23, has moved tosuch a; position in its counterclockwise movement that the voltage ofgenerator VG has risen to such an extent that the voltage of junction 32is equal to the voltage of junction 3|], the motor RM stops becausecontacts 25 and 26 move to the position shown. Since the drop ofpotential between junctions 33 and 32 is a function of the position ofarm 43 on rheostat 42, it is apparent that contact 24 will always cometo rest at a point on rheostat i9 that has a direct relation to thesetting of arm 43 on rheostat 42.

As the voltage of generator VG is increased, as above stated, the coil48 of the voltage relay will cause this relay 38 to pick up to closecontacts All and open contacts 31. The closing of contacts 47,thereafter makes the energization of contactor C independent of theposition of contacts 52.

A small counterclockwise movement of arm 23 causes the closing ofcontacts 48 of the lowvoltage limit switch 49. If the speed setting ofarm 43 is changed to a lower speed, namely'in a clockwise direction,then the junction 32' becomes more positive and in consequence contact25 will move to engage contact 50. This operation establishes a circuitfrom conductor. l8 through contacts 25 and 53, the contacts 430i limitswitch 43, field 5i, and motor RM to conductor 23. The direction ofmotor RM is thus reversed and the arm 23 moves to the left or clockwisein proportion to the extent of the clockwise setting of arm 43.

My control not only provides for effectively at will changing the speedof motor LM to any selected value either up or down from a given value,but also provides voltage regulation to compensate for changes in loadon the motor. If the load on the motor increases, the motor will operateat a different point, a lower point, on the voltage regulation curve ofthe generator. This means that the potential drop between junctions 3iand 32 increases. The result will be that the generator excitation ofgenerator VG will be increased in proportion to the greater load. On adecrease in load, the reverse will take place. The contact makingvoltmeter thus not only provides for a function to obtain the selectedspeed from a motor but also provides for Voltage regulation.

If the motor is operating at the full speed determined by the setting ofarm 43 and, the attendant wishes to go back to the slow or inchingspeed, he merely again actuates switch 6. Openin of switch 3 causesrelay 34 to drop out to open contacts 40 and M. The opening of contacts4H prevents reenerg'ization of relay 34 upon release of switch 5. Relay4 remains reenergized because its holding contacts Ill areclosed. Theenergization of contactor C is thus independent of the position ofcontacts 47.

The opening of contacts ii establishes the allresistance-in conditionfor rheostat 42.? The consequence is that arm 23. is moved to theposition shown. The motor thus slowly and smoothly decelerates from theset high speed to the inching speed. Switches 8 and 35 may thus'bealternately operated to change the speed of the motor.

either from the inchin speed to the selected high speed or from theselected high speed to the inchin speed. 2

If it is desired to stop from the inching speed, the operation of theStop switch] causes the rapid successive operation of relay 4 andcontactor C. v i

Ifthe motor LM is operating at, a selectedhigh speed andthe .Stop switchis actuated lthestopping operation is gradual. The opening of switch 1causes the relay 4 and 34 to drop out; but, since the voltage ofgenerator VG is high, the voltage relay 38 is energized and contacts 41are closed. The contactor C thus remains energized.

The deenergization of relay 34 opens contacts 4| to thus cause operationof the rheostat motor RM to move the arm to the position shown.

When the arm 23 is in the position shown, the voltage relay 38 drops outopening the circuit for coil I I of the contactor. The whole systemexcept buses I, 9 and [6, thus becomes deenergized.

From the foregoing, it will be apparent that I have provided amotor-control scheme which is very accurate and comparatively simple tobuild and is of utility in many applications requiring variable voltagecontrol.

While I have shown and described one embodiment of my invention, it isapparent that others, particularly after having had the benefit of theteachings of my invention may devise similar control schemes foraccomplishing the same or similar results. I, therefore, do not wish tobe limited to the exact showing herein made but Wish to be limited onlby the scope of the claims hereto appended.

I claim as my invention:

1. In a system of control for a direct-current motor, in combination, a,direct-current generator operating at substantially constant speed, adirect-current motor connected to said generator, a source of constantpotential direct current, a field winding for the generator, a manuallyadjustable rheostat, a motor-operated rheostat, said generator fieldwinding being connected through said motor-operated rheostat to saidsource of constant potential direct current, means for causing theoperation of said motor-operated rheostate from an all-resistance-inposition to positions including less and less resistance in the circuitof the generator field winding to thus accelerate the motor, and meansoperable when the resistance of the motor-operated rheostat hasdecreased to substantially equal the adjusted resistance value of themanually adjustable rheostat for stopping the change in resistance valueof the motor-operated rheostat.

2. In a system of control, the combination of, a source of potential, aseries circuit connected to said source, said series circuit includingan adjustable resistor and a resistor of fixed resistance value, saidadjustable resistor being adjustable to any resistance value within itsrange, a. second series circuit connected to said source, said secondseries circuit including a variable resistor having substantially thesame characteristics as said adjustable resistor, a second source ofpotential, a second resistor of fixed resistance value, said secondresistor being connected across said second source, an electromagneticdevice responsive to the difference in voltage drop across saidresistors of fixed resistance value, means for gradually varying theresistance value of said variable resistor from a given high value inthe direction of its lower values, and switching means responsive tosubstantially equal voltage drop across said resistor of fixedresistance value for efiecting a stopping of the variation of resistancevalue of said variable resistor.

3. In a system of control, a source of constant potential and a sourceof variable potential having a, common negative potential, an impedanceof fixed impedance value connected across said source of variablepotential, a variable impedance in normal use varying from a givenmaximum toward lower values of impedance, means responsive to saidvariation of impedance of said variable impedance for increasing thevoltage of said source of variable potential from a. given minimumtoward higher values, a series circuit including an adjustable impedanceand an impedance of fixed impedance value, and means responsive to thedifference in potential drop across said two impedances of fixedimpedance values for controlling the variation of the impedance value ofsaid variable impedance.

4. In a system of control, in combination, voltage producing meanshaving a first terminal at a given negative potential and a secondterminal at a given positive potential, and a third terminal, a firstcircuit across said first two terminals, means for gradually varying thecurrent flowing in said first circuit, means responsive to an increasein the current flow in said first circuit for altering the value of thepositive potential of the third terminal as a function of the currentchanges in the first circuit, a second circuit across said first twoterminals, a regulating circuit across the third terminal and the firstterminal, and means responsive to the voltage drop across said thirdterminal and a selected portion of the second circuit for controllingthe means for varying the current in the first circuit.

5. In a system of control, in combination, voltage producing meanshaving a first terminal of a given negative potential, a second terminalof a given positive potential, and a third terminal the positivepotential of which is to be varied, a first circuit including anelectromagnetic device the energization of which is to be varied and avariable impedance, means for causing a gradual diminution of theimpedance value of the variable impedance from a given maximum valuetoward a given minimum value to thus increase the energization of saidelectromagnetic device from a given minimum to a maximum value, meansresponsive to the rise in energization of said electromagnetic devicefor increasing the positive potential of the third terminal, a secondcircuit including an impedance of fixed impedance value and anadjustable impedance connected across said first and second terminal,and means responsive to the positive Voltage of the third terminal inrelation to the voltage drop across said impedance of fixed impedancevalue for controlling the means for causing a gradual diminution in theimpedance of the variable impedance.

6. In a system of control, in combination, voltage producing meanshaving one terminal at a given negative potential and a second terminalat a given positive potential, and a third terminal, a first circuitacross said first two terminals, means for gradually varying the currentflowing in said first circuit, means responsive to an increase in thecurrent flow in said first circuit for altering the potential of thethird terminal as a function of the current changes in the firstcircuit, a second circuit across said first two terminals, a regulatingcircuit across the third terminal and the first terminal, and meansresponsive to the voltage drop across said third circuit and a selectedportion of the second circuit for controlling the means for varying thecurrent in the first circuit.

7. In a system of control, the combination of, a generator driven at aconstant speed, a motor connected in a loop circuit with the generator,an exciter driven at a constant speed and excited to producesubstantially a constant voltage, said exciter having its negativeterminal connected to "the negative terminal of the'generator, saidgenerator having a field winding and -a rheostat therefor connected inseries circuit across the exciter terminals, a motor for controlling theresistance value of the rheostat, a circuit including a resistor havingsubstantially the same resistance value as the generator field winding,and an adjustable rheostat having generally the same electricalcharacteristics as the first-mentioned rheostat connected in parallel tothe enerator field winding and its control rheostat, asecond resistor,having substantially the same resistance value of the first-mentionedresistor, connected across the generator terminals, and means responsiveto the difierence in voltage drop across said'two resistors forcontrolling the operation ofthe motor for actuating the rheostat of thegenerator field winding.

8; In a system of control, the combination of, a generator driven at aconstant speed, a motor connected in a loop circuit with the generator,an exciter driven at a constant speed and excited to producesubstantially a constant voltage,

said exciter having its negative terminal conneoted to the negativeterminal of the generator, said generator having a field winding and arheostat therefor connected in series circuit across the exciterterminals, a motor for controlling the resistance value of the rheostat,a circuit including a resistor having substantially the same resistancevalue as the generator field winding, and an adjustable rheostat havinggenerally the same electrical characteristics as the first-mentionedrheostat connected in parallel to the generator field winding and itscontrol rheostat, a second resistor, having substantiallythe sameresistance valueof the first-mentioned resistor, connected acrossthegenerator terminals, a contact making voltmeter having one terminalconnected to the positive terminal of the generator and its otherterminal connected at the junction of the adjustable rheostat andsecond-named resistor Whereby said voltmeter hand is actuated from aneutral position either clockwise or counterclockwise depending on thesign of the difference of the voltage drop across said two resistors,and means responsive to the operation of said voltmeter to cause themotor for the generator field rheostat to operate either inone-directiono1z the other'ditrection or not at all depending 'on thepositionof the voltmeter hand.

9. In a system of control, the combination-of, a generator driven at aconstant speed, a motor connected-in a loop circuit with the generator,an exciter driven at a constant Speed and ex? cited to producesubstantially a constant voltage, said exciter having its negativeterminal connected to the negative terminal of the generator, saidgenerator having a field winding and-a-rheostat therefor connected-inseries, circuit across the exciter terminals, a motor forcontrolling-the resistance value of the rheostat, a circuit including aresistor having substantially the same resistance value as the generatorfield. winding, and an adjustable rheostat havinggenerally the sameelectrical characteristics as the first-mentioned rheostat connected inparallel to the: generator field winding and its control rheostat, asecond resistor, having substantially thesame-resistance value of thefirst-mentioned resistor, connected across the generator terminals, acontact making voltmeter having one terminal connected to the positiveterminal of the generator and its other terminal connected at thejunction ofthe adjustable rheostat and second-named,res-istor wherebysaid voltmeter hand is actuatedfrom a neutral position either clockwiseor counterclockwise depending on the sign of the difference of thevoltage drop across said two resistors, and means responsive to theoperation of said voltmeter to cause the motor for thegeneratorvfieldrheostat to operate either in one direction-orthe other direction or notat all depending'on the position of the voltmeter hand, and means foropen-circuiting the adjusting circuit-.ofthe adjustable rheostat wherebythe voltage ofthegenerator will be caused to be a minimum.

FREDERICK D SNYDER;

REFERENCES CITED Name Date Howe Apr.- 5, 1932 Number

